1. Field of the Invention
The invention relates generally to a technique of distributing content such as video and sound to a client.
2. Description of Related Art
In recent years, with the rapid development of the Internet, the WWW system, in which content that is a file written in HTML (Hyper Text Markup Language) is transferred to a client from a WWW (World Wide Web) server, using HTTP (Hyper Text Transfer Protocol), to display the content via a WWW browser, has been widely utilized.
Also, with broadband lines to normal households and of high-performance PCs (Personal Computers) becoming widespread, a service performing streaming distribution of high-quality and large-capacity video using a network is now realized more easily. In this streaming distribution, a client (client terminal) transmits a request message to a distribution server, and in response, the distribution server transmits video data to the client together with a relevant header. Here, the client can interpret the data to reproduce it.
The current problem of streaming distribution is that a distribution server has throughput limitations. More specifically, there is a limit to the number of distributions for each distribution server. Therefore, in order to distribute content with sufficient quality in response to requests from many clients, plural distribution servers need to be arranged to respond to requests from the clients.
Examples of a method of arranging plural servers include a method of simply arranging servers in parallel and allocating clients' requests to the servers, and a method of, under the control of servers, sharing content files and reading data from the shared content files.
However, these methods cause a reduction in performance due to insufficient storage capacity for storing content and multi-read processing.
From the above, an invention has been proposed in which: a proxy server is provided at the preceding stage of a distribution server (origin server) having original content; content often requested by a client is stored as cache data in the proxy server; and when a request for the same content arrives at the proxy server from the client, the proxy server responds to the client without accessing the origin server and also stores a packet, as cache data, in a storage device connected to the proxy server (see JP2004-070860 A).
Also, an invention has been proposed in which: a proxy server is provided at the preceding stage of an origin server; the proxy server, having received a distribution request from a client, transfers the distribution request to the origin server; the origin server provides a packet in the distribution request with a protocol header, and also distributes the packet provided with the protocol header to the proxy server; the proxy server, having received the packet, changes the destination of the packet transmitted from the origin server to the client and distributes the packet to the client, and also captures a streaming packet; and data (hint file), in which a protocol header, transmission time, etc., are recorded, and content data (packet file) are stored, as cache data, in storage (see JP2005-295467 A).